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object Day03 {
private fun addLists(l1: List<Int>, l2: List<Int>) = l1.zip(l2).map { it.first + it.second }
private fun valueOfBits(bitList: List<Int>) = bitList.reduce { acc, bit -> acc * 2 + bit }
private fun invertBits(bitList: List<Int>) = bitList.map { bit -> 1 - bit }
private fun mostCommonBits(input: List<List<Int>>): List<Int> =
input
.reduce(::addLists)
.map { bit -> if (bit.toDouble() / input.size >= 0.5) 1 else 0 }
private fun selectByBitCriteria(
input: List<List<Int>>,
comparisonCriteria: (currentList: List<List<Int>>) -> List<Int>
): List<Int>? {
var list = input
var index = 0
while (list.size > 1 && index < list[0].size) {
list = list.filter { e -> e[index] == comparisonCriteria(list)[index] }
index += 1
}
return list.getOrNull(0)
}
fun part1(input: List<List<Int>>): Int =
mostCommonBits(input)
.let { gammaBits ->
val epsilonBits = invertBits(gammaBits)
return valueOfBits(gammaBits) * valueOfBits(epsilonBits)
}
fun part2(input: List<List<Int>>): Int {
val oxygenRating = selectByBitCriteria(input) { mostCommonBits(it) }!!
val scrubberRating = selectByBitCriteria(input) { invertBits(mostCommonBits(it)) }!!
return valueOfBits(oxygenRating) * valueOfBits(scrubberRating)
}
}
fun main() {
val testInput = readInputAsBitLists("Day03_test")
check(Day03.part1(testInput) == 198)
check(Day03.part2(testInput) == 230)
val input = readInputAsBitLists("Day03")
println(Day03.part1(input))
println(Day03.part2(input))
}
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